1. Field of Application
The present invention relates to a control apparatus that controls an electrical generator (referred to in the following simply as a generator) of a motor vehicle, and in particular to a control apparatus which derives and utilizes the speed of rotation of the rotor of an alternator that constitutes the generator.
2. Prior Art Technology
A generator of a motor vehicle is generally an alternator (typically, a 3-phase alternator) having a rotor that is driven by a belt and pulleys, or gears, from the vehicle engine. In the prior art, a type of control apparatus for a generator of a vehicle is known, that is implemented as an electronic control unit (hereinafter referred to as an ECU), with the ECU performing control in accordance with the speed of rotation of the alternator rotor (referred to in the following simply as the speed of rotation of the generator) or in accordance with the engine speed, assumed to be synchronized with that of the generator. In general, the ECU also controls the operation of the vehicle engine. Since the engine speed, and hence the generator speed of rotation, each vary in accordance with the running condition of the vehicle, it is necessary to measure the engine speed of rotation and the generator speed of rotation at frequent intervals, to enable accurate control by the ECU.
Such a control apparatus may include some form of detector device for directly detecting rotation of the generator, to thereby obtain a detection signal for use in measuring the speed of rotation of the generator, with such a signal being referred to in the following as the rotation speed measurement signal SNA. The rotation speed measurement signal SNA may be used internally by the ECU to measure the speed of rotation of the generator, for example as described in Japanese Patent Laid-open No. 62-99876, referred to in the following as reference document 1.
Alternatively, the control apparatus may include a sensor for detecting the engine rotation, with a resultant sensor signal being utilized internally by the ECU to measure the engine speed of rotation, and with control of the generator being performed based on the engine speed of rotation. This is described for example in Japanese Patent Laid-open No. 58-162739, referred to in the following as reference document 2.
With the technology of reference document 1, it is necessary to measure the speed of rotation of the generator each time the ECU is to perform control relating to the vehicle engine or the generator. Hence, the ECU must perform such measurement operations very frequently, so that the processing load that must be handled by the ECU is substantially increased, and the control performance of the ECU is thereby lowered.
On the other hand, with the method of reference document 2, it is not necessary to measure the speed of rotation of the generator at frequent intervals, since that can be calculated based on the engine speed of rotation. Such an ECU must in any case measure the engine speed, in order to control the engine operation, so that the problem of increased processing load on the ECU is avoided if the engine speed of rotation is used to derive the speed of rotation of the generator.
However in order to calculate the speed of rotation of the generator based on the engine speed of rotation, the ECU must use accurate information concerning the pulley ratio (or the gear ratio) by which the generator is driven from the engine. Such information must therefore be stored beforehand in each ECU, so that it is necessary to use a number of different types of ECU that store respectively different sets of such information, relating to various different vehicles. Thus, such a method has the disadvantage that the number of different types of ECUs that must be manufactured is increased.
It will be understood from the above that although the present invention is described from the aspect of a control apparatus for controlling the generator of a motor vehicle, such a control apparatus will in general be an apparatus such as an engine ECU which controls both the generator and the engine of the vehicle.